Described below is an excitation device for an electric machine. In particular, the electric machine is a synchronous machine, which preferably, but not exclusively, uses a superconducting inductance as the field winding.
In electric machines with an electrically excited and moved secondary part (rotor), such as in particular in the case of synchronous machines (SM), the excitation losses can advantageously be reduced to a minimum by implementing the exciter winding as a high-temperature superconducting (HTS) winding. For this purpose, however, the cooling of the superconductor to a temperature range of below 80K, i.e. at least the temperature of liquid nitrogen, is necessary.
In the case of a design with superconductors, any input of heat via mechanical contacts should be avoided as far as possible. Mechanical contacts, such as sliprings or the like, are involved as a result of the maintenance required and moreover are susceptible to wear. For this reason, the excitation power, the monitoring and regulation information is advantageously transmitted in contactless fashion, i.e. inductively, to the rotor. During operation of the machine, it is necessary to convert the de-excitation energy into heat when the field windings in the machine are demagnetized.
Known excitation devices for a superconducting winding typically include a contactless energy transmission path, a contactless control or regulating signal transmission path to a stationary control and regulating unit, and an actuator for impressing a voltage and a freewheeling circuit. In this case, the transformer in particular functions inductively.
EP 1 247 324 B1 proposes a unidirectional inductive energy transmission, a “rotating transformer” including two pot-type cores with ring windings and axial flux guidance being provided as inductive operating means. In this case, the pot-type cores can move toward one another about the common axis.
Inductively functioning operating means are described in detail in the dissertation: Albert Esser: “Berührungslose, kombinierte Energie- und Informationsübertragung für bewegliche Systeme” [Contactless, combined energy and information transmission for mobile systems] ISBN 3-86073-046-0; ISEA, RWTH Aachen 1992. The statements in the dissertation are aimed at contactless bidirectional energy and data transmission in robot joints.
DE 41 33 001 A1 has furthermore disclosed “photoelectric transmission” for the transmission of both energy and data. While the energy transmission has a deficient power density, data can be transmitted in a manner which is very insensitive to faults and free of potential. Such systems are commercially available. Such unidirectional energy transmission for exciting a superconducting winding needs a passive resistor on the cooled rotor for de-excitation, which resistor converts the excitation energy into heat, which then needs to be dissipated. Both the input of heat and the passively and exponentially decaying excitation are in this case undesirable.
Against the background of the related art, an improved excitation device for a winding which can be used in electric machines.